The present invention relates to a mineral acid slurry of a benzidine derivative having high stability in which the benzidine derivative is suspended in a dilute mineral acid.
Benzidine derivatives constitute the primary disazo components used in the production of dyes and also yellow, orange and blue diszo pigments applied for printing ink and plastics. 3,3'-Dichloro-4,4'-diaminobiphenyl, which is representative of the benzidine derivatives, is suspected as a cancer causing agent throughout the world and various regulations for its handling are established in various countries.
3,3'-Dichloro-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl and 3,3'-dimethyl-4,4'-diaminobiphenyl are listed on the group-1 substances in the laws on prevention of hazards due to specified chemical substances of the industrial safety and health laws in Japan. For the manufacture and handling of them, it is required that employees wear proper protective clothing, that they be handled in a closed system, that they be supplied as a wet product and that a local ventilation system be provided for decontamination. These protections are necessary in order to avoid human exposure to these materials.
Under the regulations, a benzidine derivative as a product is shipped generally in the form of a wet powder containing water or acid to avoid raising dust.
However, as the above method, i.e., the wet powder form, is not a complete solution to the problem of dust and there remains a possibility that operators might be exposed to the benzidine derivative. In order to decrease human exposure due to dusting of the product, it is necessary to make the benzidine derivative into a slurry form and to transport it in a closed container or a tank lorry, to convey the slurry by pumping and to handle it in an even more closed system.
Further, in the case of a benzidine derivative which is solid at room temperature being made into slurry, the stability of the slurry is important.
As for a method for obtaining a slurry of 3,3'-dichloro-4,4'-diaminobiphenyl having stable dispersibility, for example, U.S. Pat. No. 4,559,160 has proposed specifically defining the hydrochloric acid concentration and the 3,3'-dichloro-4,4'-diaminobiphenyl content in the slurry. Further, in Japanese Laid-open Publication No. Sho. 64-42456, in addition to the definition of the hydrochloric acid concentration and the 3,3'-dichloro-4,4'-diaminobiphenyl content, it has been proposed to add a nonionic surface active agent to the slurry.
In the above two patent publications, the solid component in the slurry, 3,3'-dichloro-4,4'-diaminobiphenyl, partially settles out and is thus separated from its mother liquor, and it solidifies in a few days.
In order to store the slurry, the settled solid must be soft enough to be easily agitated and homogeneously re-dispersed into the slurry. However, in the above two patent publications, the settled solid becomes too hard to be agitated and therefore, there still remains a problem that the slurry needs to be continuously agitated for smooth discharge.